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BELL SYSTEM TECHNICAL JOURNAL 



by the delay circuit in the Type A vodas was not recorded. However, 

 the effect of a transmission delay of 20 milliseconds is shown by sub- 

 tracting 20 milliseconds from the point at which operation occurred. 

 This is indicated on the oscillogram for both devices. It is concluded 

 that on this wave the syllabic device without a delay circuit would 

 give about the same clipping as the Type A vodas with its delay circuit. 

 Figure 8 indicates that the Type A would be better for stronger speech 

 and the Type B would be better for weaker speech. The advantage of 

 a delay circuit in either case is evident. 



It is evident from this analysis that the reason for using delay 

 circuits is not primarily because the relays are slow in operating. 

 When the sensitivity is limited by noise, clipping of initial consonants 

 can occur with infinitesimal operating times. One way of reducing 

 the clipping is to use long releasing times so that the relays remain 



OPERATE POINT 

 TYPE B 



TIME 



"""•"' " y 



OPERATE POINT 

 TYPE A 

 Fig. 9 — Oscillogram of the word "SIX," illustrating clipping and its reduction by a 

 delay circuit in the transmission path. 



operated between syllables. This has the disadvantage of making it 

 harder for the opposite talker to break in. To avoid this difficulty, 

 the relays in the vodas are given releasing times that permit the 

 distant speech to break in about one sixth of a second after a United 

 States talker ceases to speak. 



One advantage of delay circuits is to reduce the clipping of initial 

 consonants and thus permit using short releasing times, thereby 

 making it possible to reverse the circuit more readily. In addition, 

 delay circuits permit using a lower relay sensitivity which has two 

 advantages. First, more noise can be tolerated without causing false 

 operation. Second, more received volume can be delivered without 

 the echoes causing false operation of the normally blocked trans- 

 mitting side. 



The advantage of artificial delay of various amounts has been 

 determined by using different types of normally blocked arrangements 



